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These types of devices usually require some sort of sampling time to display actual values....just like a fluke DVM. You are probably missing the 'peak' current due to the response time of the display. FWIW, it probably doesn't matter.

Most folks don't realize how small of a current they actually use from the residential service panel. Generally 8-12 amperes (or less) unless air conditioning or hot tub equipment is operating.

late to this thread.......this comes up every 2 months or so, I advise people:

Check the back of your equipment or the owners manual (online for planning purposes)

It has this info, max current needs, here my EP2500 uses 9.5A @ 120V

Mike,
Just fyi, the EP2500/4000 can pull ~2400watts, or ~20amps with test tone type material. It's dependent on the load presented across the speaker terminals on the amp. Whereas encountering voltage clipping into 4ohms, would be draw double the current as hitting clipping into an 8 ohm load. When I say "test tone type" material, what I'm referring to is the larger LF effects that accompany contemporary BD/DVD releases. Some of these are much more similar to test tones, than the spectral characteristics associated with music releases. Some HT LF effects, such as those found in HTTYD (How to Train Your Dragon), are nearly as wide as the spec, 3hz-120hz, very high in level, torturous and long in duration. Hence, a bit more related to test tones, than the typically less demanding music. Other effects, such as the outstanding gunfire/blasts that occur in the fanstastic Open Range, are very high in level, however they're very brief and clearly deliniated. Very demanding of a system's transient capability, but possess no longer term demands on current delivery.

So, being a class H amplifier, with a multi rail voltage supply, efficiency is in the area of 83%. (2000/2400). As I illustrated above, the amperage drawn at clipping from the wall, depends on the load across the amps terminals. Taking this a step further, as one lowers the impedance even more, approaching a short circuit, the amp will pull so much current that the amps on-board breaker, or the branch circuit breaker feeding the system (or both) will open up,...preventing physical damage.

---

Mike as you pointed out, the mfrs. nameplate rating of 9.5amps. I'm not sure how they obtain that, various mfrs. get their numbers in different manners. And as pointed out previously, one would only typically hit the maximum draw in very brief moments, quick enough to be inconsequential to the breaker. However, voltage drop can be an insidious effect,....robbing a system of it's capability at the exact moment it needs it most. It's a subtle, subtractive non-linearity, similar to compression. That said it's not real obvious until one is shown otherwise. So being mindful to stay away from your branch circuits maximum allowable current, helps retain system impact during playback of the huge, taxing low frequency effects. Just as other components posses linear envelope, so does the branch circuit feeding your sub system. Once again, headroom is the answer.

Mike, I'm fully aware that you are well versed in this, as I believe we've discussed this. However, for others so interested, diminishing the effects of voltage drop is facilitated by larger gauge wiring, and shorter runs. If needed, a great system tweak is a dedicated circuit, with up-sized wiring. Assuring tight connections throughout the entire run, from the breaker, to the receptacle, is paramount. Nearly all failures/problems occur due to connections that work themselves lose.

Hmmm... Power is ideally constant for max power, independent of the load. The output current (I) and voltage (V) into the speaker) change, but wall power (V and I) should not... There will of course be some variation, but an amp that puts out 100 W into 8 ohms and 200 W into 4 ohms draws (essentially) the same power from the wall with either load.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley

Oops, my bad, I was thinking about the voltage, duh. I said current changes (doubles) with the lower load impedance and then started a side conversation and lost my Watt train. How I could say we go from 100 W to 200 W without changing the current is beyond me, not enough drugs I guess... Actually, I was trying to explain off-line how the power should quadruple when we bridge an amp and got interrupted in the middle of writing, and just flat-out blew it when I finished the post because my mind was clearly elsewhere.

Or maybe I was thinking of that cold fusion supply in the basement, yeah that's it...

Three-plus decades of engineering down the drain. Need to stick with the GHz stuff...

Here's what I meant to write:

Hmmm... Voltage is ideally constant for max power, independent of the load. The output current (I) into the speaker changes, but supply voltage (V) should (ideally) not... There will of course be some variation, but an amp that puts out 100 W into 8 ohms and 200 W into 4 ohms draws (essentially) double the power (current) from the wall with the lower load.

P = V*I = V^2 / R = I^2 * R

With fixed voltage from the supply, halving R doubles the power and thus doubles the current.

Where I wanted to go was to point out that an ideal amp (fixed voltage rails, infinite current drive ability) will double its power when the load resistance is halved, and quadruple the power when bridged for the same load impedance since the voltage is doubled. IME people do not understand where the "extra" power comes from in bridged mode since it is more than doubled... I am frankly at a loss for how I wrote what I did; senility.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley

Hmmm... Power is ideally constant for max power, independent of the load. The output current (I) and voltage (V) into the speaker) change, but wall power (V and I) should not... There will of course be some variation, but an amp that puts out 100 W into 8 ohms and 200 W into 4 ohms draws (essentially) the same power from the wall with either load.

Since we have so many design options to choose from, amp current drain can vary quite a bit. Lets only talk about SS amps. Generally power amps have output stages that are either class AB or class D (switchmode). Their power supplies are either single voltage traditional supply, multiple supply (Class G or H), or switchmode.

Output stages and power supplies can be mixed or matched so one could have a switchmode output stage with a single voltage traditional supply, or a class AB output stage with a power supply that is both switchmode and also has multiple output voltages.

The worst from an efficiency standpoint is the class AB output stage with a single traditional power supply. The most efficient is a switchmode output stage with a switchmode power supply.

The efficiency of any power amplifier varies depending on the relationship between the instantaneous output power level and its power ratings. The worst case for most power amps is somewhere between 20 and 40% rated power and below, and the most efficient operation is usually achieved at full output.

The load affects the power that the amp draws from its power source. Obviously low impedance loads cause more power to be drawn. However, few if any speakers cause current drain that compares with test bench operation, due to the fact that their impedance is generally higher than their ratings at most frequencies in the audible range.

The other issue is duty cycle. It is unlikely that a power amp that is amplifying normal music with low distortion is running at 100% duty cycle. It is more likely running close to 10-15% duty cycle, even if it is running just below clipping on the peaks. In reality, most of the time most peoples amps are not drawing that much more current than when they are idling.

That brings up the issue of idling current. The term "Class AB" covers a wide range of idling current drain situations ranging from minimal to heavy based on some designer's desire to run in Class A (full conduction of both sides of the output stage) up to a large number of watts.

Put this laundry list of variables together and estimating a number for amps becomes a dizzying proposition, even for trained and experienced professionals. Compare that to what you find out in a few minutes with a Kill-A-Watt or something like it and you can easily become a fan of real-world measurements!

IME most people vastly overbuild the power line facilities for their audio systems, particularly in dedicated facilities (e.g. HT room). Since the raw materials are usually pretty inexpensive, and installation costs are usually nominal, I don't lose a lot of sleep over this! ;-)

On balance, you'll probably be amazed what you can get away with on a dedicated 15 amp circuit.

Having a circuit breaker trip in the middle of a crescendo or chase scene is a real bummer!

Ok, if the current stays the same, ... doubling the 100, to 200 watts, where does the other 100 watts come from?

The power line. Most power amps put about 140% as much power (max) into 4 ohms as 8 ohms because the power supply losses significantly drop the voltage from the power supply. Losses through the output transistors also increase.

Quote:

The additional 100 watts manifests from the higher current being drawn.

P=EI

You double the P, I doubles

Right, but that analysis presumes at number of things that aren't always true.

As I mentioned before, no real world power amp, even the ones with 6,011 output devices and big black heavy toroids and power supply capacitors from here to San Diego actually put twice as much current into half the ohms. I've suspected this for a long time, and a week with a 5-figure high end power amp renowned for this sort of thing, sitting on my test bench verified this.

This monster amp was rated at 125 watts into 8 ohms, and 250 watts into 4 ohms. It weighed just under 100 pounds. In comparison the 125 wpc (my rating based on testing) Behringer A500 put out just under 200 watts into 4 ohms, if memory serves, and weighed about a dozen pounds. On the bench the monster actually delivered more like 190 watts into 8 ohms, 270 watts into 4 ohms, and tripped out a dedicated 20 amp circuit delivering something like 380 watts into 2 ohms. There was also a strong frequency dependency into its actual power output, and it put out much more power below 400 Hz than above. At 20 Hz it did crazy good things and vastly overpowered its ratings to even a greater degree.

The monster was a very interesting thing. While it was vastly overpriced for the actual performance it provided, it looked to me like it was designed to shred just about any conventionally designed power amp you compared it to (e.g. a Bryston), while driving just about any load you hooked it to, and simultaneously keep people from frying midranges and tweeters while doing unexpectedly good things with subwoofers.

The monster was the amp I might design for rich dilettantes who think they are audio systems integrators and magazine reviewers with too much time on their hands to subjectively compare it to other amps into a variety of speakers. Until you measured it quite thoroughly, it would seem to violate any number of laws of physics. ;-)

Three-plus decades of engineering down the drain. Need to stick with the GHz stuff.......

No problem, I fully understand. A few days ago in the DIY forum, I mistakenly corrected someone and mixed up and reversed high pass, for low pass. I mean things cannot get much more self explanatory,....and still I screwed it up. If that wasn't bad enough, I did it correcting someone,...that had it right! I've designed and implemented HP and LP filters for audio applications, both active and passive, for decades!

Quote:

Originally Posted by DonH50

With fixed voltage from the supply, halving R doubles the power and thus doubles the current.

Where I wanted to go was to point out that an ideal amp (fixed voltage rails, infinite current drive ability) will double its power when the load resistance is halved, and quadruple the power when bridged for the same load impedance since the voltage is doubled.

I know exactly what you mean. Something akin to this Boulder monoblock monster. It doubles it's wattage into subsequent halving of load impedances.

Boulder had a tiny 10x10 booth at Cedia circa 2000. I was working the show walking quickly, and upon seeing that amp from the rear, it stop me in my tracks,...turning around and meeting the Boulder rep and discussing the thing etc. They didn't demo their stuff, merely displayed their big statement amp. pretty interesting visit I had. That big blue Hubble pin and sleeve connector caught my eye, and blew me away. This is industry standard high current connector, and I'd never seen one on an consumer/HiFi amplifier,...so kudos to them.

This amplifier product, is as if the Pentagon mil spec'd an amp to be made,..I mean in person the thing is truly phenomenal. It is said all amplifiers operating within their linear envelope sound very similar. It's only when they encounter design limits, ie incoming signal slew rate, clipping, etc, when they exhibit significant differences. Well, this one's linear envelope is pretty damn BIG!

Amazing, what do you suppose prof. Shockley would think about that bad boy? More akin to nuke power, than transistorized

------------

Quote:

Originally Posted by mtbdudex

FOH,
Back in 2007 when I was wiring my basement and doing load calculations, I followed this code check book.......

.......and this load analysis method per NEC, which includes using the actual nameplate ratings as the "worst case" for major appliances.......

......Hence I assumed the same for all elect nameplate ratings when doing my HT load calculations.......

Mike,

Typical mfrs. nameplate rating for operational voltage, and maximum current draw are dead on accurate. For whatever reason (I'm guessing duty cycle/crest factor, pink noise, etc., blah blah), they don't place the actual max current draw. The manner in which they work, a nominal operational impedance of 8 ohms, "X" amps will be drawn. Then, with subsequent impedance lowering, closer and closer to short circuit, the amperage increases. But, they choose to place the 8 ohm current at clipping on the nameplate. Approximately 9-10 amps is max needed when an EP2500/4000 hits max power, at clipping onset, at an eight ohm stereo load. But this is sustained, wide-band low frequency content. typical to program material, not very. But, as I pointed out in the post above, some of the big LF effects are wide-band, and sustained, so one must be mindful of this scenario.

That said, Arny is right. Typically, your amps aren't pulling much for very long. Smaller breakers would generally suffice, but my personal caveat is voltage drop. Even though a breaker will pass huge amounts of "audio" type current, physics isn't short cutted when it comes to the properties of Ohm's Law. The copper, or aluminum (I certainly hope not) that resides between your LF amplifiers and your panel-board, needs to be sized so that voltage drop is not a concern. Rarely is a potential choke-point so easily addressed, and put to bed, as is the case with up-sizing of the branch circuits feeding your amplifiers, LF or otherwise.

Still very impressive. At 18kWRMS and 85% efficiency, they are dissipating 2700 watts in a single 9U slot. I’m betting those are dual 48V blowers and blow and sound like two hair dryers.

I do see they get realistic and throttle Pout back for real-world duty-cycles, as Arny mention. The cite ¼ power as 4.5kW. 80% eff. This represents 'highly compressed techno 'music’. AKA pink noise. Ha!

Hmm. 18kW across a 4 ohm load. That's 268A. What kind of cables and connectors do they use? Garden hose?

Looks from the data sheet like it's single-phase, 95 - 265 V. Idle power is 235 VA; they do not list ful power numbers (just 1/8 and 1/4). Hard to see how the thing can get enough input power to reach its peak power... Draws about 15 A/230V or 30A/115V at just 1/4 power; assuming it tracks linearly, that's 60A/230V and 180A/115V. They list an AMP CPC 45A power connector and 10 AWG cord... Neutrik NL4MD speaker connectors (a 4-pin connector; they use two pins in parallel for + and -).

Looks from the data sheet like it's single-phase, 95 - 265 V. Idle power is 235 VA; they do not list ful power numbers (just 1/8 and 1/4). Hard to see how the thing can get enough input power to reach its peak power... Draws about 15 A/230V or 30A/115V at just 1/4 power; assuming it tracks linearly, that's 60A/230V and 180A/115V. They list an AMP CPC 45A power connector and 10 AWG cord... Neutrik NL4MD speaker connectors (a 4-pin connector; they use two pins in parallel for + and -).

I recall a story about musicians in the army, they would burnout the barrel of their automatic weapons on a regular basis..turned out the only solution was to mount a small holder on the end of the barrel and mount a small piece of sheet music there for the user to see...it has a few notes, and most importantly, some rests...

With a 10awg cord, they'd need to give the bassist an ampacity chart..

Specially if I were the bassist...The only bass that's too loud or powerful is....um, um,

jn

Some discuss because they can. Others attack because they cannot. (unknown attribution)A good man knows his own limitations...(Dirty Harry)Lead, follow....or get out of the way..

Looks from the data sheet like it's single-phase, 95 - 265 V. Idle power is 235 VA; they do not list ful power numbers (just 1/8 and 1/4). Hard to see how the thing can get enough input power to reach its peak power... Draws about 15 A/230V or 30A/115V at just 1/4 power; assuming it tracks linearly, that's 60A/230V and 180A/115V. They list an AMP CPC 45A power connector and 10 AWG cord... Neutrik NL4MD speaker connectors (a 4-pin connector; they use two pins in parallel for + and -).

"Hard to see how the thing can get enough input power to reach its peak power"

The PDF doc shows pink noise 1/4 rated power, line consumption at 25a@230v. The specs state 225v peak output, 125a peak output. So those peak numbers can back off .707 or so.

From that point, with the state of the art SMPS, and a trick, high speed class D output stage, throw in the manner in which caps charge when not needed, and they're at the ready for the next signal peak. Typically, caps recharge 120 times a second, this with both positive and the negative swings of the 60Hz mains. With an amplifier of this degree of apparent sophistication, I'm not sure how frequently the caps recharge.

How the output numbers are generated, I'm not sure but I'd bet they're legit. The pro market is pretty straight up with regard to specs such as these. I can't say much more about the operation, because I'm certainly not smart enough to design an amp of this type,..or any type

Finally, be mindful how over-current protection works. This is an aspect I do fully understand. Huge amounts of current easily jump around the breaker for extended periods of time (to prevent nuisance/start up trips). Oftentimes, depending on the breaker type, a breaker will allow 7 times its rated amount for up to 1-2 seconds. Then at that point, the curve slowly trends back toward 3-4 times it's rated amount at 10 seconds, and ultimately up to twice it's amount still at 30 seconds. So clearly a capable, robust amplifier, can easily be supplied with ample current amounts to ride out most any program material this side of test tones.

What I find amazing is the front to back level of adaptability, sophistication, power capability, connectivity, etc. Up to 300v tolerant, power factor correction PS, inrush protection, full DSP DA/AD, with 16 parametric filters per channel, shelving etc, 48dB Xovers, remote monitoring of load impedance, mains voltage/current, temps. Menu for setting max output voltage, max mains current draw,...that's very cool.

Still very impressive. At 18kWRMS and 85% efficiency, they are dissipating 2700 watts in a single 9U slot. I'm betting those are dual 48V blowers and blow and sound like two hair dryers.

I do see they get realistic and throttle Pout back for real-world duty-cycles, as Arny mention. The cite ¼ power as 4.5kW. 80% eff. This represents 'highly compressed techno 'music'. AKA pink noise. Ha!

Hmm. 18kW across a 4 ohm load. That's 268A. What kind of cables and connectors do they use? Garden hose?

As long as they use it to play unclipped music, it probably will never draw more than 1/4 of maximum rater power.

I understand your outlet (and breaker) will probably support the peaks, and in the real world that's good enough, but for testing they must have a heckuva feed. Maybe they only test to 1/4 power because they only have a 30 A dedicated line in-house?

A number of new class D amps are interleaving and/or upping the rate in both the supply and the output. Wouldn't surprise me if they weren't doing the same, recharging those caps quickly, though switching that much current quickly is a challenge...

I noticed they also have feedback loop to compensate speaker wire loss. They threw in a lot of cool stuff!

If I sent 18 kW throuigh my system I am not sure the house would still be standing. Pretty sure the speakers wouldn't!

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley

I noticed they also have feedback loop to compensate speaker wire loss. They threw in a lot of cool stuff!

I can see how that may be handy. Remote sense I presume?

I miscalculated the current for 18kW/4ohms earlier. My value was V, not I. Glad I caught it. Load V/R is 67A. 10ga Cu wire is ~1mOhm/ft. ~450W of power dissipated in I2R loss for a 50' run of 10ga carrying 67A. I'd imagine this fans out to multiple parallel runs however in an arena? usage.

"Hard to see how the thing can get enough input power to reach its peak power"

Finally, be mindful how over-current protection works. This is an aspect I do fully understand. Huge amounts of current easily jump around the breaker for extended periods of time (to prevent nuisance/start up trips). Oftentimes, depending on the breaker type, a breaker will allow 7 times its rated amount for up to 1-2 seconds. Then at that point, the curve slowly trends back toward 3-4 times it's rated amount at 10 seconds, and ultimately up to twice it's amount still at 30 seconds. So clearly a capable, robust amplifier, can easily be supplied with ample current amounts to ride out most any program material this side of test tones.

A standard 15 or 20A panel breaker (thermal-magnetic) will have two protection elements. The long time element will allow overcurrent for a period of time according to its long time curve....typically we test at three times rating and find the breaker will 'trip' in less than 10 seconds for the QO style. The instantaneous element will 'trip' the breaker at approximately 10 times the frame rating (150-200 amperes) for this style. See the attached trip curve for a QO frame breaker. This of course all depends upon the breaker manufacturers' tolerances at the time of manufacture

Appears to be consistent with FOH's data... Thanks for the curve! I'd forgotten about those, too long since my electrician days...

@dlarsen: I did not look closely but I would assume you are right, a little wire attached at the load as a sense line. I did that with my first servo sub build, and extended it to an amp design but found in my case (100 - 500 W peak, big cables, short runs) it made little difference. For something like that beast and a big reinforcement system (long runs) it makes sense to get a higher effective damping factor at the speakers.

I was going to challenge the IR loss until I realized there are two wires going to the speakers... Already made one stoopid mistake in this thread, geez!

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley

How about doing it the right way and adding up the total "watts" required to run the equipment? You most likely have 120 volt service on a 15 amp breaker. That equates to a total safe load of 1800 watts on that breaker. One must remember there is very likely other items, lights and plugins on the single breaker as well that could draw watts at the same time your AVR/equipment is in operation.
Each of your components will list the "watts" usage for each. Just add it up. Now, the other side of it is the referenced wattage numbers are typically max draw and you will typically never see that max load thus just because you total them all up and it exceeds say 1800 isn't a show stopper. I would suggest a power center that tells you current amp draw. That way you can tell the exact amount of power you are pulling on your circuit. IE: if it displays a draw of 5 amps that would be a total of 5 x 120 = 600 watts thus we'll within your say 1800 limit.

Cheers

^^^ I like this answer. I want to add a comment....lots of people out there are confused about the word "watts", especially when talking about power consumption. Example: my five channel separate power amplifier's manual says power consumption 1400 watts. The output however is 150 watts x 5 channel RMS.